242 NORTH AMERICAN INDEX FOSSILS. 



142. P. speciosa Hall. (Fig. 294, d-e.) 



Devonic-Lower Carbonic. 



Broadly ovate with obtusely angular cardinal extremities. 

 Pedicle valve regularly arcuate from beak to front and abruptly 

 depressed between the umbo and the narrow, short ears. Surface 

 marked by fine concentric striae and on the ears by a few short 

 wrinkles. The whole body of the shell covered with about 25 

 concentric rows of spine-bearing tubercles. 



Portage, Chemung and Kinderhook of New York, Ohio, Iowa, 

 Nevada. 



143. P. arcuata Hall. (Fig. 294,/, g.) Lower Carbonic. 

 Length exceeding width. Pedicle valve very gibbous with 



greatly incurved beak. Differs from P. navicella in its larger size 

 and in the almost entire absence of spines on the radial costse, only 

 a few scattered ones occurring. 



Kinderhook of Iowa, Ohio and Missouri. 



144. P. pyxidata Hall. (Fig. 294, h.) Lower Carbonic. 

 Width greater than length. Hinge line shorter than greatest 



width of shell. Pedicle valve somewhat flattened and slightly re- 

 curved at the cardinal extremities; umbo narrow. Surface of both 

 valves marked with lamellose growth lines ; spine-bearing radiat- 

 ing ridges at times present on pedicle valve. 

 Kinderhook of Illinois and Missouri. 



145. P. shumardana Hall. (Fig. 294, i.) Lower Carbonic. 

 Hinge line about equalling the greatest width of shell. Pedicle 



valve very convex, gibbous in the middle and towards the umbo ; 

 cardinal extremities flattened. Brachial valve moderately concave. 

 Surface of both valves covered with fine concentric striae and 

 strong spine bases. Differs from P. pyxidata in the absence of 

 lamellose growth lines. 



Kinderhook of Missouri, Iowa and Ohio. 



146. P. concentrica Hall. Lower Carbonic. 

 Small. Hinge line scarcely equalling the greatest width of 



shell. Brachial valve deeply concave, almost geniculate in front. 

 Surface of older portion of valve covered with strong concentric 

 wrinkles and a few tubercles ; the younger portion with elongate 

 spine bearing ridges. 



Kinderhook of Ohio, Indiana, Iowa and Michigan. 



